Grey seals numbers were reduced by hunting to the point of being considered rare in eastern North America through the 1950s. The largest grey seal breeding colony is now located on Sable Island. In the early 1960s, several hundred pups were born on the island. Since then the numbers of pups born has increased exponentially and by 2010 some 62,000 were born. Estimates birth and survival rates, from long-term observations on marked individuals, coupled with estimates of pup production from aerial photographic survey are used to estimate Sable Island herd at about 500,000 in 2013. Reproductive performance of females improves with age but senescence is evident in females in their late twenties and older. Survival rates of adults are high, but drop off rapidly in males aged 20+ and in females aged 30+ years. Adults fitted with satellite tags and from which blubber biopsies were taken provide an understanding of the foraging distribution and diet. Males and females exhibit strong seasonally-dependent, sex segregation in foraging distribution and diet with males using deeper and more seaward areas to the southwest of Sable Island and females using area shoreward and to the northeast. Along with population size these data provide an estimate of population prey consumption and the growing ecological foot print of this large predator on and off the Island. Sable isotope analysis indicates that grey transport significant quantities of marine nutrient to the island through faeces and carcasses which influence the flora and ultimately the horses of Sable Island.